Mohammed T. Abou-Saleh

Principles and Practice of Geriatric Psychiatry.Editors: Professor John R. M. Copeland, Dr Mohammed T. Abou-Saleh and Professor Dan G. BlazerCopyright & 2002 John Wiley & Sons LtdPrint ISBN 0-471-98197-4 Online ISBN 0-470-84641-020Long-term Outcome Studiesof Psychiatric Disorders: Methodological Issuesand Practical Approaches to Follow-upAnn Stueve, John Toner and Anne V. QuismorioColumbia University Stroud Center, New York, USAWhat are the long-term outcomes of various types of psychiatricdisorders? How do individuals, interacting with their environments,shape the course and consequences of mental illness? Whatenvironmental, personal and illness characteristics are associatedwith recovery and improvement? Are such characteristics disorderorlife stage-specific? A growing number of long-term follow-upstudies have begun to address such questions. Their results bothconfirm and challenge accepted wisdom. Long-term outcomes ofschizophrenia, for example, do seem to be worse on average thanthose of affective disorders 1 ; at the same time, however, outcomesof schizophrenia are remarkably varied, undermining conceptionsof its course as progressively deteriorating and chronic 2 . Substantiveresults from long-term follow-up studies are included inother chapters of this volume (see specific disorders). This chapterfocuses instead on several basic methodological issues—caseidentification, co-morbidity, choice of comparison groups, samplerepresentativeness and measurement issues—as they pertain tolong-term follow-up studies (see refs 3–6 for elaboration). Ourpurpose is to alert readers to issues that potentially influence theinterpretation and comparison of results. Issues associated withthe statistical analysis of longitudinal data are beyond the scope ofthis chapter and are not included (see refs 6–8 ).There are two basic types of follow-up investigations: (a)prospective studies, in which the investigator defines a sample onthe basis of current attributes (e.g. psychiatric or exposure status)and follows the sample forward in time; and (b) retrospectivecohort designs, in which the researchers define the sample on thebasis of some past characteristic (e.g. hospital admission during aspecified time period, participation in an earlier study) and thenreconstruct their subsequent life course up to some later point intime, using records, retrospective interviews, etc. 3 Retrospectivecohort (or ‘‘catch up’’) designs require less time to complete thanprospective studies covering a similar duration, but are morelimited by the availability and quality of extant data and problemsof recall. Both types of investigations have been used to elucidatethe long-term course 9 and outcomes of psychiatric disorders 1 . Theissues discussed below apply to varying degrees to both types ofinvestigation.CASE IDENTIFICATIONCase identification refers to the criteria and procedures used todetermine what constitutes a case of the disorder under study andaddresses the question, ‘‘long-term outcomes of what?’’ 10 . Withoutexplicit specification of what constitutes a case, similaritiesand difference in observed outcomes across studies are difficult tointerpret. For example, observed differences may reflect discrepanciesin diagnostic practice; observed similarities may beillusory. Case identification is particularly problematic in longtermfollow-up studies, where baseline data and diagnoses oftenpredate the introduction of modern diagnostic systems andstandardized assessment tools. One way in which investigatorshave dealt with this problem is to rescore baseline data (e.g. fromhospital charts, case notes or interviews) using one or morecurrent diagnostic systems (e.g DSM–III–R, ICD–10) and toselect and compare cases based on these newer diagnoses 4 . Thispractice allows for comparison of outcomes using differentnosologies and, insofar as criteria for inclusion and exclusionare reported, facilitates comparison of results across studies. Suchbenefits of rescoring, however, remain dependent on the qualityand comparability of baseline data. Signs and symptoms that werenever attended to or recorded obviously cannot be recovered, andtheir absence potentially introduces error into the rescoringprocess.CO-MORBIDITYA second issue concerns co-morbidity (i.e. the co-occurrence oftwo or more psychiatric disorders in an individual) and addressesthe question, ‘‘to what extent are observed outcomes due topsychiatric conditions other than the one under study?’’ 5,22–25 .What appear to be differences in outcomes of schizophrenia, forexample, may be due in part to differences in the prevalence andcombination of secondary conditions. Here, too, the assessmentof co-morbidity and its ramifications is particularly difficult inlong-term follow-up studies, because outcomes may be influencednot only by secondary disorders recorded at baseline but also bythe onset and recurrence of other disorders between baseline andfollow-up. While some assessment tools [e.g. Schedule forAffective Disorders and Schizophrenia—Lifetime(SADS-L)] generatethe data needed to make lifetime diagnoses, sampleattrition and reliance on informants may impede reliableassessment of interim conditions for substantial numbers ofsubjects.Principles and Practice of Geriatric Psychiatry, 2nd edn. Edited by J. R. M. Copeland, M. T. Abou-Saleh and D. G. Blazer&2002 John Wiley & Sons, Ltd